Shearbølgerne

Shearbølgerne, also known as shear waves or transverse waves, are a type of seismic wave that travels through the Earth's interior. Unlike compressional waves (P-waves), shear waves cause particles in the rock to move perpendicular to the direction of wave propagation. Imagine a rope being shaken up and down; the wave travels horizontally along the rope, but the rope itself moves vertically. This characteristic motion is what defines a shear wave.

Shear waves are slower than P-waves and cannot travel through liquids. This is because liquids lack the rigidity to transmit shear motion; their molecules can slide past each other freely, offering no resistance to the perpendicular displacement. Consequently, when seismic waves encounter the Earth's liquid outer core, shear waves are stopped, while P-waves can pass through, albeit with a change in velocity and direction.

This behavior of shear waves has been crucial in understanding the Earth's internal structure. By observing seismic data from earthquakes, scientists can identify "shadow zones" where shear waves are absent, indicating the presence of the liquid outer core. The study of shear waves has also provided insights into the properties of the Earth's mantle and crust, helping to map out different rock types and their physical states. Their slower speed also means they arrive at seismograph stations after the initial P-wave arrival, allowing seismologists to distinguish between different wave types and analyze the Earth's interior in detail.